This invention pertains to hollow grinding machines, and more particularly to a mechanism for easily and accurately controlling the bevel angle of the grinder.
Hollow grinders are commonly used for sharpening tool blades, and typically include a tool-rest for maintaining a desired orientation of the blade relative to the grinding wheel. This orientation determines the grinding angle (or bevel angle) with respect to the longitudinal axis of the tool blade.
The tool-rest is typically adjustable with two or more degrees of freedom to facilitate adjustment of the height and attitude of the tool blade, while maintaining a proper air gap between the tool-rest and the grinding wheel to prevent operator injury. Simultaneously achieving a desired bevel-angle and air-gap can be both difficult and time consuming, and most hollow-grinding machines have no mechanism for determining the bevel angle that will be achieved with a given height-attitude setting. The problem is exacerbated by the fact that the bevel angle not only varies with height-attitude setting, but also with grinding wheel radius, which decreases with use. Thus, the bevel angle obtained for a particular height-attitude setting on one wheel will be different if the tool is ground on a wheel of different radius. Accordingly, what is desired is a hollow grinder with a bevel angle control that is easily adjustable and that provides accurate bevel angle control despite variations in grinding wheel radius.
The present invention is directed to an improved hollow grinder bevel angle control wherein a height-attitude linkage mechanism restricts the height and attitude motions of an adjustable tool-rest to a prescribed relationship, and a scale on a stationary portion of the grinder cooperates with a pointer on the height-attitude linkage mechanism to indicate a relationship between achieved bevel angle and grinding wheel radius. According to the invention, the linkage mechanism is implemented with a stationary link and three movable links, defining a parallelogram. The first and second movable links are rotatable about fixed pivot points at one end, and the third movable link is coupled to the other (free) ends of the first and second movable links. The fixed pivot point for the first movable link is co-axial with the grinding wheel, and the tool-rest is supported on a shaft coupling the first and third links. The tool-rest is mounted for slidable adjustment parallel to the longitudinal axis of the first link to permit adjustment of the gap between the tool-rest and the periphery of the grinder wheel.
The pointer is mounted for rotation with the first link about its fixed pivot point, and is user-adjustable so that the distance from the fixed pivot point to the tip of the pointer coincides with the radius of the grinder wheel. The bevel angle scale is stationary with respect to movement of the linkage mechanism, and arranged so that the tip of the pointer sweeps across the scale as the linkage mechanism is adjusted through its full range of movement. The indicia on the scale reflect the height-attitude relationship defined by the linkage mechanism, such that the indicia coinciding with the tip of the pointer denotes the achieved bevel angle. A tool-rest lock mechanism selectively couples the linkage mechanism to the grinder housing to maintain a selected height/attitude relationship.
With the above-described apparatus, achieving a desired bevel angle merely involves adjusting the pointer length based on grinding wheel radius, raising or lowering the tool-rest via the linkage mechanism until the pointer tip coincides with the corresponding indicia on the bevel angle scale, and then locking the tool-rest in place with the tool-rest lock mechanism.